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Studying how lipids regulate fertilization, we have recently discovered a new step in fertilization, and a possible new pathway to cancer. Using sperm and eggs from Xenopus laevis, we conduct in vitro fertilization to study the biochemical and biophysical steps of how the sperm and egg fuse their membranes, activate phospholipase D1b to produce phosphatidic acid (PA) which binds and activates Src tyrosine kinase. We also study how phospholipase C isoforms are activated by Src and lipids like PA. Finally, we study how IP3 is produced and how it releases intracellular calcium at fertilization. Through a calcium sensitive dye, we record an increase in intracellular calcium first at the sperm-egg binding site, and a wave is then generated to travel across the zygote. We use HPLC and Mass spec separation with evaporative light scattering detection for lipid analysis, and phosphospecific western analysis with our dual laser Odyssey system to quantify active enzymes involved in fertilization.
Ph.D., Washington State University
B.S., Biology, Ohio State University
Using an NIH-recognized model system, the Xenopus oocyte/egg, my lab has examined the role of lipid signaling during fertilization, insulin action, and the induction of cell division. We published the first general lipid signaling survey of fertilization in the Journal of Lipid Research in 2008. This paper was selected for highlighting over other articles in the journal issue by the American Society for Biochemistry and Molecular Biology Today (Dec. 2008). The ASBMB article discussed the fact that, in spite of numerous lipid events (fusion, lipase activation), this is the first such survey.
After demonstrating the activation of phospholipase C during fertilization, we have found evidence for the activation of other lipases (sphingomyelinase, autotaxin and phospholipase D), and suggest that they play a role in fertilization. We have extensive evidence that phosphatidic acid, a lipid product of phospholipase D1b activation at fertilization, is able to bind and stimulate Src tyrosine kinase (Src activation is a known event in Xenopus fertilization). This work, which has resulted in one publication (2014), two manuscripts, shows that elevation of phosphatidic acid leads to Src activation of phospholipase C gamma activation, IP3 mass increase and release of intracellular calcium- the latter is the central event of fertilization. The work draws upon my 35 years of experience in Xenopus biology, my 28 years of lipid signaling expertise, our collection of specialized lipid equipment and protocols (e.g., evaporative light scattering mass detector, HPLC protocol and mass spectrometer for lipid analysis, lipase assays, etc).
Highlighting a few,more recent publications:
2015 Bradley J. Stith. Phospholipase C and D regulation of Src, calcium release and membrane fusion during Xenopus laevis development. Developmental Biology 401(2):188–205. A review with original data, invited by Editor Richard Harland (Berkeley).
2014 Activation of Src and release of intracellular calcium by phosphatidic acid during Xenopus laevis fertilization. Developmental Biology 386:165-180. Ryan C. Bates, Colby P. Fees, William L. Holland, Courtney C. Winger, Khulan Batbayar, Rachel Ancar, Todd Bergren, Douglas Petcoff and Bradley J. Stith.
2014 Ryan C. Bates, Bradley J. Stith, Karen E. Stevens and Catherine E. Adams. Reduced Chrna7 expression in mice is associated with increases in hippocampal parvalbumin and glutamate
decarboxylase-67 (GAD67) and altered levels of GABAA receptor subunits. Neuroscience 273 (2014) 52–64.
2012 Ryan Bates, Bradley J Stith, Karen Stevens. Chronic central administration of valproic acid: Increased pro-survival phosphor-proteins and growth cone associated proteins with no behavioral pathology. Pharmacology, Biochemistry and Behavior 103:237-244.
2008 Douglas W. Petcoff, William L. Holland, Bradley J. Stith. "Lipid levels in sperm, eggs, and during fertilization in Xenopus laevis." Journal of Lipid Research 49:2365-2378.
2008 Bradley J. Stith. "Metformin action on the insulin receptor, other tyrosine kinases and phosphatases. In Metformin: Mechanistic Insights towards New Applications." Editors: Gilles Mithieux and Nicolas Wiernsperger. Pgs 59-80. Transworld Research Network publishers, Kerala, India.
2006 Ken-ichi Sato*, Yasuo Fukami, and Bradley J. Stith.* "Signal transduction pathways leading to Ca2+ release in vertebrate fertilization: lessons from Xenopus eggs." Seminars in Cell and Developmental Biology. 17: 285-92. *corresponding authors.
2004 Bradley J. Stith. "Use of animation in teaching cell biology." Cell Biology Education3:8-15, 2004.
2004 William Holland, Thomas Morrison, Ying Chang, Nicolas Wiernsperger, and Bradley J. Stith. "Metformin (Glucophage) inhibits tyrosine phosphatase activity to stimulate the insulin receptor tyrosine kinase." Biochemical Pharmacology 67:2081-2091.
2003 William L. Holland, Erin C. Stauter, and Bradley J. Stith. "Quantification of phosphatidic acid and lysophosphatidic acid by HPLC with evaporative light scattering detection." Journal of Lipid Research 44:854-858.
2002 Ayala Luria*, Vaida Vegelyte-Avery*, Brad Stith§, Nelly M. Tsvetkova*, Willem F. Wolkers*, John H. Crowe*, Fern Tablin1, and Richard Nuccitelli.*2 From the *Section of Molecular and Cellular Biology, University of California, Davis, CA 95616, 1Department. Of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, and the §Department of Biology, University of Colorado-Denver, Denver, CO 80217. "Discrete Microdomains in the Plasma Membrane of Xenopus laevis eggs." Biochemistry. 41:13189-13197.
2000 Thomas Morrison, Leslie Waggoner, Laura Whitworth-Langley, and Bradley J. Stith. "Nongenomic action of progesterone: activation of Xenopus oocyte phospholipase C through a plasma membrane-associated tyrosine kinase." Endocrinology, 141: 2145-2152.
2000 Stith, Bradley J. "Use of a web site to enhance a Biology lecture course."Technological Horizons in Education, 27:20-28.
2000 Stith, Bradley J., Jennifer Hall, Patrick Ayes, Leslie Waggoner, James Moore, Walt Shaw. "Quantification of major classes of Xenopus phospholipids." Journal of Lipid Research41: 1448-1454.
BIOL 3611: General Cell Biology
BIOL 3612: Cell Biology laboratory
BIOL 4064/5064: Advanced Cell Biology
BIOL 4054/5054: Developmental Biology
BIOL 4550/5550: Cell Signaling